Addition of warnings about shells choices in FRF and FODF fit

[frheault]

Quick description

This is a manual extraction from my work on StatefulImage once I realized that it is very easy to provide inaccurate shells in our scripts. While mrtrix take hard decisions (always pick the highest shells) in SSST, we do not. We trust the user, but we should at least warn users. There is a heuristic to determine if the provided shells are too far apart. If the delta between shells is higher than the smallest non-zero: warning
(A file with b800 and b1200 is fine, but b700 and b2000 are too big)

In addition to the problem, but to the 'weird' FODF being produced by our SSST when shells were too far apart, there was a warning in our tracking script that detected these 'weird' FODF as peaks, so I also improved the heuristic to distinguish peaks (often of length 15) from FODF (at SH order 4, also length 15). However, when FRF/FODF process with appropriate shells, this was rarely an issue.

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Type of change

Check the relevant options.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Provide data, screenshots, command line to test (if relevant)

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Checklist

• My code follows the style guidelines of this project (run autopep8)
• I added relevant citations to scripts, modules and functions docstrings and descriptions
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I moved all functions from the script file (except the argparser and main) to scilpy modules
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[codecov]

Codecov Report

❌ Patch coverage is 74.35897% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.49%. Comparing base (b8699e9) to head (6d947be).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1336      +/-   ##
==========================================
- Coverage   72.51%   72.49%   -0.02%     
==========================================
  Files         300      300              
  Lines       26105    26139      +34     
  Branches     3662     3671       +9     
==========================================
+ Hits        18929    18949      +20     
- Misses       5633     5640       +7     
- Partials     1543     1550       +7     

Flag	Coverage Δ
smoketests	69.70% <58.97%> (-0.03%)	⬇️
unittests	14.07% <64.10%> (+0.06%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
Scripts	75.25% <100.00%> (-0.02%)	⬇️
Library	69.17% <72.97%> (-0.02%)	⬇️

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[arnaudbore]

Few comments, It's going to be a fast merged PR.

[arnaudbore]

GTG